Adrenaline, Insulin, Hormones, Tropism, and Reproduction
Hormones: Adrenaline and Insulin
A hormone is a chemical substance secreted by an endocrine gland. It is carried by the blood, which alters the activity of one or more specific target organs and is then destroyed by the liver.
Chemical Control of Metabolic Activity by Adrenaline
Adrenaline is a hormone secreted by the adrenal glands. When you are frightened or excited, your brain sends impulses along a nerve to your adrenal glands. This makes them secrete adrenaline into the blood.
Adrenaline helps you to cope with danger:
- It increases heart rate, supplying oxygen to the brain and muscles more quickly, increasing energy for action (fighting, running, etc.).
- It contracts blood vessels in the skin and digestive system, so they carry very little blood, supplying blood back to vital organs (brain and muscles).
- It stimulates the liver to convert glycogen to glucose, increasing glucose release into the blood by the liver, providing extra glucose for muscles to help muscles contract.
Insulin
Insulin is a hormone made in the islets of Langerhans in the pancreas. It plays a vital role in the homeostatic control of blood sugar concentration. The pancreas will secrete insulin into the blood when the blood glucose concentration gets too high. There are many cells in the body with insulin receptors, but the main target tissue for insulin is the liver.
What is a Hormone?
- A hormone is a chemical substance produced by a gland and carried by the blood, which alters the activity of one or more specific target organs. They are chemicals that transmit information from one part of the organism to another and bring about a change.
- The glands that produce hormones in animals are known collectively as the endocrine system.
- Endocrine glands have a good blood supply because when they make hormones, they need to get them into the bloodstream (specifically the blood plasma) as soon as possible so they can travel around the body to the target organs to bring about the response.
- Once a hormone has been used, it is destroyed by the liver.
Adrenaline
- Adrenaline is known as the “fight or flight” hormone, as it is produced in situations where the body may be in danger.
- It causes a range of different things to happen in the body, all designed to prepare it for movement (i.e., fight or flight).
- These include:
- Increasing blood glucose concentration for increased respiration in muscle cells.
- Increasing pulse rate and breathing rate so glucose and oxygen can be delivered to muscle cells, and carbon dioxide taken away from muscle cells more quickly.
- Diverting blood flow towards muscles and away from non-essential parts of the body, such as the alimentary canal; again, to ensure the reactants of respiration are as available as possible.
- Dilating pupils to allow as much light as possible to reach the retina so more information can be sent to the brain.
Tropism
Tropism refers to responses by part of a plant towards or away from a stimulus coming from one direction (growth movement).
- Positive: Towards stimulus.
- Negative: Away from stimulus.
- Phototropism: Growth in response to light.
- Geotropism: Growth in response to gravity.
Reproduction
Reproduction is a process where a new living organism of the same species is produced; this prevents extinction.
- Sexual reproduction: Two parents are needed. It is the fusion of haploid nuclei of two gametes to form a diploid zygote. Offspring are genetically different. It involves fertilization.
- Asexual reproduction: Does not involve gametes or fertilization. Only one parent is needed. Offspring are genetically identical.
Sexual Reproduction in Plants
The flower is the organ in charge of sexual reproduction. You need male and female gametes, which fuse to make a zygote. Bees pollinate flowers, making reproduction possible.